Vehicles, including wheeled vehicles, are typically suspended to absorb shock encountered while traversing uneven terrain. Wheeled vehicles often include one suspension assembly per wheel so that each wheel may absorb shock independently. In many cases each such suspension assembly comprises both a spring portion and a damping portion. The spring portion may consist of a mechanical spring, such as a wound helical spring, or it may comprise a pressurized volume of gas. Gas is often used because it is light weight. Unlike typical simple mechanical springs, gas springs have non-linear spring rates. Compound mechanical springs may also have non-linear rates. A single gas spring has a spring rate that becomes exponential at compression ratios greater than about sixty percent. As a practical matter that can mean that a shock absorber including a gas spring rapidly becomes increasingly stiff just past the middle of its compressive stroke. Such increased stiffness over an extended length of the stroke is often undesirable (e.g. harsh riding vehicle).
In performing the dampening function, the damping mechanism of a shock absorber also creates resistance of the shock absorber to movement (e.g. compression and/or rebound). Unlike the spring which resists based on compressive displacement, fluid dampers usually have resistance to movement that varies with displacement rate (i.e. velocity). Under some circumstances, fluid dampers may not react quickly enough to account for large disparities in the terrain encountered by the vehicle.
What is needed is a shock absorber dampener that offers resistance to movement as desired while becoming compliant to large disparities encountered by the vehicle over rough terrain.